The present invention relates to concrete compositions, concrete formulations for producing concrete compositions when mixed with water, cement compositions, concrete articles, methods of manufacturing concrete compositions and methods of manufacturing concrete articles. Particularly, although not exclusively, the present invention relates to semi-dry concrete compositions for use in the production of concrete articles for use in block paving applications.

Concrete is used in many areas of the construction industry, for example in the construction of buildings, and bridges. Pre-formed concrete bodies, such as paving slabs and blocks, are known for providing surfaces and pre-formed concrete bodies are also employed for decorative purposes or as ready made elements of structures such as buildings.

There are known a number of concretes having differing compositions depending upon the application in which the concrete is used. Such concrete compositions comprise cement, fine aggregate, coarse aggregate and water and optionally other additives. Cement, fine aggregate ('fines') and coarse aggregate can be provided as a concrete formulation which when mixed with water provides a concrete composition. This composition then sets to produce concrete.

There are known concrete compositions which, when set, result in concrete having considerable strength. However, such concretes may still not be as strong as might be desired for some applications. Concrete is often employed in applications where it is subjected to considerable forces. In order to compensate for this, concrete bodies may need to be of a substantial size to provide the required strength. Additionally, concrete bodies may be employed in situations where they are subjected to considerable wear and tear, such as weathering. Known concretes may not withstand such wear and tear as well as may be desired. One such application in which the concrete articles formed from the concrete compositions are subject to considerable forces and considerable wear and tear is in block paving: where concrete blocks are used to provide a surface over which heavy vehicles may frequently travel. Further, whilst many different mixes with different properties are known and in use, high strength mixes having a low cost factor are few and far between and highly sought after.

Concrete compositions may be formulated not only with their properties when set in mind, but also to suit the production technique that the composition will undergo to form articles. One such production technique typically used to produce block paving and walling is referred to as a semi-dry Vibro-Pressed process, which involves moulding the concrete composition under combined vibration and hydraulic pressing. In such a process the concrete composition is "just moist", with a consistency measured by producing a cohesive ball when compressed by squeezing together in the hands. This is also often referred to as "earth-moist" concrete and typically has a water to cement ratio in the range of 0.30 to 0.45.

The present invention aims to address at least one disadvantage associated with known concrete whether discussed herein or otherwise. Preferred embodiments aim to provide high strength concrete articles at relatively low cost.

According to a first aspect of the present invention there is provided a cement composition for use in a concrete composition, the cement composition comprising: cement; at least one cement alternative; wherein the or each cement alternative is a powder, and wherein the cement and the cement alternative are present relative to each other in an amount of between about 40:60 (in % by weight) and 60:40 (in % by weight).

Advantageously, it has been found that the substitution of an amount of cement with a cement alternative according to the present invention provides a concrete composition having excellent strength and density characteristics. A further advantage of a concrete composition made using a cement composition of the present invention is that cement, being an expensive commodity, can be in part replaced by a cement alternative, which may be a cheaper material. Accordingly, a cement composition according to the present invention can be used to provide concrete articles having significant financial advantages over prior art concrete articles. Suitably, the cement comprises Portland Cement. The Portland Cement may be as described in BS EN 197: CEM I. The cement preferably comprises Ordinary Portland Cement (OPC).

Preferably, the at least one cement alternative is substantially chemically unreactive toward water. By the term substantially chemically unreactive toward water it is meant that contact with water does not lead to any chemical reaction. Preferably, the at least one cement alternative does not retain water following exposure thereto and subsequent drying.

Preferably, the at least one cement alternative is selected from one or more of the following materials: limestone powder, dolomite limestone powder, granite powder, pulverised fuel ash powder, bottom furnace ash powder, paper ash powder. In a most preferred embodiment, the cement alternative comprises limestone powder.

Preferably, the limestone powder comprises at least about 90% by weight calcium carbonate (CaCO ₃ ), more preferably at least about 93% by weight calcium carbonate and most preferably at least about 95% calcium carbonate.

By the term "wherein the or each cement alternative is a powder" it is mean that the or each cement alternative has a particle size of less than 1 mm.

Preferably, the cement alternative has an average particle size of less than 150μm, more preferably less than 75μm, yet more preferably less than 45μm.

References herein to particle size refer to particles passed through a sieve as is well known in the art. Accordingly, references to "average particle size of less than ..." should be understood as at least 50% by weight able to pass through a sieve of the corresponding size. For example, if at least 50% of particles (by weight) pass through a sieve with holes of 150μm, then the average particle size is less than 150μm.

In a preferred embodiment, the particle size of the cement alternative is such that at least 90% by weight, more preferably at least 99% by weight passes through a 150μm sieve. In a preferred embodiment, the particle size of the cement alternative is such that at least 80% by weight, more preferably at least 90% by weight passes through a 75μm sieve.

In a preferred embodiment, the particle size of the cement alternative is such that at least 60% by weight, more preferably at least 75% by weight passes through a 45μm sieve.

Preferably, the cement alternative has a particle size distribution such that at least 99% by weight passes through a 150μm sieve, at least 90% by weight passes through a 75μm sieve, and at least 75% by weight passes through a 45μm sieve.

Preferably, the cement and the cement alternative are present relative to each other in an amount of between about 42:58 (in % by weight) and 58:42 (in % by weight). More preferably, the cement and the cement alternative are present relative to each other in an amount of between about 45:55 (in % by weight) and 55:45 (in % by weight). More preferably, the cement and the cement alternative are present relative to each other in an amount of between about 48:52 (in % by weight) and 52:48 (in % by weight).

In a most preferred embodiment, the cement and the cement alternative are present relative to each other in an amount of about 50:50 (in % by weight).

According to a second aspect of the present invention there is provided a concrete formulation comprising a cement composition, the cement composition comprising: cement; at least one cement alternative; wherein the or each cement alternative is a powder, and wherein the cement and the cement alternative are present relative to each other in an amount of between about 40:60 (in % by weight) and 60:40 (in % by weight) and, one or more aggregates.

The concrete formulation comprises one or more aggregates. The aggregates may comprise fine aggregates (fines) and/or coarse aggregates.

The aggregates may comprise material such as from naturally occurring or marine sources together with any crushed rock fines or crushed stone material. Alternatively or additionally, the fine aggregates may be derived from suitable recycled or waste material.

Preferably, fine aggregates have a typical average particle size of between about 1 mm and 4mm, whereas, preferably, coarse aggregates have a typical average particle size of between about 4 and 20mm.

Examples of suitable aggregates include but are not restricted to sand and limestone.

Preferably, the concrete formulation comprises aggregates in an amount of between 20 and 95 wt% of the overall formulation.

Suitably, the concrete formulation comprises fine aggregates in an amount of between 20 and 95 wt% of the overall formulation.

The concrete formulation may comprise the coarse aggregate material in an amount of between 20 and 95 wt % of the overall formulation.

The cement composition may be present in the concrete formulation in an amount of between about 5 to 30% by weight of the overall formulation. Preferably, the cement composition is present in the concrete formulation in an amount of between about

10% to 20% by weight of the overall formulation, more preferably between about 12% and 18% by weight and most preferably between about 15% and 17% by weight.

Preferably, the balance of the above percentages by weight in the overall formulation (ie. to make 100% in total) is comprised of aggregates and, optionally one or more admixture.

Reference herein to "by weight of the overall formulation" refers to the dry weight of the concrete formulation.

The concrete formulation may comprise an admixture agent for aiding consolidation of the formulation during concrete manufacture. Suitably, the admixture agent comprises a polycarboxylate. The admixture agent may be any suitable polycarboxylate. The admixture may be present in an amount of between about 0.01% to 1 % by weight of the overall formulation, more preferably between about 0.1 % to 0.5% by weight of the overall formulation and most preferably between about 0.2% and 0.3% by weight of the overall formulation.

Preferably, the concrete formulation comprises less than 5% by weight (with reference to the weight of the overall formulation) of ground granulated blast furnace slag, more preferably less than 3% by weight, more preferably less than 1 % by weight and most preferably less than 0.1 % by weight. In a particularly preferred embodiment, the concrete formulation comprises substantially no ground granulated blast furnace slag.

References herein to ground granulated blast furnace slag, refer to ground granulated blast furnace slag as described in British Standard BS EN 15167.

The concrete formulation may comprise other additives as are known in the art. For example, the concrete formulation may comprise fillers, pigments, etc.

Preferably, water is added to the concrete formulation to form a concrete composition. Therefore, according to a third aspect of the present invention there is provided a concrete composition comprising: a cement composition, which cement composition comprises: cement; at least one cement alternative; wherein the or each cement alternative is a powder, and wherein the cement and the cement alternative are present relative to each other in an amount of between about 40:60 (in % by weight) and 60:40 (in % by weight), the concrete composition further comprising water.

Preferably, the water is present in the concrete composition such that the wateπcement composition ratio is less that about 0.5 (by weight), more preferably less than 0.4 (by weight), yet more preferably less than 0.3 (by weight).

Preferably, the wateπcement composition ratio is between about 0.2 to 0.4 (by weight), more preferably, the wateπcement composition ratio is between about 0.2 and 0.35. Most preferably, the wateπcement composition ratio is between about 0.2 and 0.3. Reference herein to the wateπcement composition ratio refers to the total water available in the composition, including that available from the aggregates (where present), divided by the powder composition (the sum of the cement and the cement alternative and any other powders).

Preferably, the concrete composition comprises the concrete formulation of the second aspect. In such an embodiment, it will be understood that the cement composition of the third aspect and the cement composition of the second aspect are the same.

The invention also extends to concrete articles and concrete structures made in accordance with any of the above listed compositions and formulations, as well as to methods of manufacturing concrete compositions and methods of manufacturing concrete bodies and structures using the above mentioned compositions/formulations.

Therefore, according to a further aspect of the present invention there is provided a concrete article formed from a concrete composition, the concrete composition comprising a cement composition, the cement composition comprising: cement; at least one cement alternative; wherein the or each cement alternative is a powder, and wherein the cement and the cement alternative are present relative to each other in an amount of between about 40:60 (in % by weight) and 60:40 (in % by weight).

Preferably, the concrete composition comprises a concrete formulation according to the second aspect of the invention.

Preferably, the concrete composition is a concrete composition according to the third aspect of the invention.

Preferably, the article comprises a block, for example, for use in block paving.

All of the features contained herein may be combined with any of the above aspects and in any combination. The invention will now be described with reference to the following non limiting examples.

EXPERIMENTAL

In the following examples, limestone powder was used to replace a portion of the usual cement content and the amount of water used varied. Details of the compositions of the examples are given in Table 1.

TABLE 1 (All amounts given in kg)

KEY:

Aggregate 1 = Tilbury Dock Sand (0 to 4mm)

Aggregate 2 = Askoy Granite (2 to 6mm)

CD

Aggregate 3 = Askoy Granite (2 to 6mm)

Pigment = CanCarb Black (Carbon Black pigment)

Limestone Powder = Trucarb 285 Limestone Powder (99% by wt passing through 150μm sieve, 90% by wt passing through 75μm sieve and 75% by wt passing through 45μm sieve)

Cement = Ordinary Portland Cement (OPC)

GGBS = ground granulated blast furnace slag

Admix 1 = VP Bio (a polycarboxylate admix, commercially available from Grace Construction Products)

Admix 2 = EU 06/13 (a polycarboxylate admix, commercially available from Grace Construction Products)

Water 1 = Water added to the mixture

Water 2 = Water available within the aggregates

WaterPowder ratio= Water 1 + Water 2 / sum of powders (Limestone powder, Cement and GGBS)

RESULTS

The example formulations as shown above in tablei were formed into blocks using the Vibro-Press method described in the preamble, cured for >10 hours (actual was 14 hours) at a temperature of >24°C and humidity >80%.

The blocks were then tested for strength and density at 7 days and 28 days and the results shown in the table below.

^* Strength measurements provided are tensile splitting strengths, measured according to BS EN 1338: 5.3.3 Annex F, and given in units of N-mm ^"2

^** Density measurements provided are measured according to BS EN 12390-7 and are given in units of kg-m -3

Portland Cement:

Limestone Powder:

• Limestone Synonyms:

Limestone, calcium carbonate, precipitated calcium carbonate, ground/pulverized calcium carbonate, PCC< GCC, calcite, limestone,

10 crushed marble, ground limestone, lime, chalk, whiting, champagne chalk, French chalk, albacar, and aeromatt

Limestone Formula:

15 CaCO ₃ Limestone Description:

Produced by crushing, grinding, precipitation, and classifying high purity, white, calcite limestone

Typical purity of Limestone Powder is 95 - 99.9% pure properties of Limestone Powder are described below:

In the above examples, some specific examples of formulations have been set out. However, it should be appreciated by the man skilled in the art that the invention is not limited to these particular ratios and formulations. In fact, a range of formulations may in general be used and fall within the scope of the present invention.

Discussion

As shown above, concrete compositions according to the present invention have a significantly lower amount of cement than prior art formulations, approximately 25% less cement in fact. A person skilled in the art would expect that this significant reduction in cement would lead to a much lower strength in the resulting concrete article. However, as shown in Table 2, this is not the case. In fact, on the contrary, the concrete articles show improved strength characteristics. Furthermore, the compositions of the present invention allow the wateπpowder ratio to be significantly reduced, which a person skilled in the art would expect to lead to detrimental results.

As shown in the table above, concrete compositions made in accordance with the present invention have higher tensile strength, but lower densities than prior art concrete compositions. Further, because the cement content is lower than traditional block formulations, the overall cost of the formulations is also lower.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.